[SelectionDAG] Add generic implementation for @llvm.expect.with.probability when optimizations are disabled (#117459)

Handle \@llvm.expect.with.probability in SelectionDAGBuilder, FastISel,
and IntrinsicLowering in the same way \@llvm.expect is handled, where
the value is passed through as-is. This can be reached if the intrinsic
is used without optimizations, where it would otherwise be properly
transformed out.

Fixes #115411 for SelectionDAG. A similar patch is likely needed for
GlobalISel.

Author: antangelo

llvm/lib/CodeGen/IntrinsicLowering.cpp

@@ -236,8 +236,10 @@ void IntrinsicLowering::LowerIntrinsicCall(CallInst *CI) {
     report_fatal_error("Code generator does not support intrinsic function '"+
                       Callee->getName()+"'!");
 
-  case Intrinsic::expect: {
-    // Just replace __builtin_expect(exp, c) with EXP.
+  case Intrinsic::expect:
+  case Intrinsic::expect_with_probability: {
+    // Just replace __builtin_expect(exp, c) and
+    // __builtin_expect_with_probability(exp, c, p) with EXP.
     Value *V = CI->getArgOperand(0);
     CI->replaceAllUsesWith(V);
     break;

llvm/lib/CodeGen/SelectionDAG/FastISel.cpp

@@ -1456,7 +1456,8 @@ bool FastISel::selectIntrinsicCall(const IntrinsicInst *II) {
 
   case Intrinsic::launder_invariant_group:
   case Intrinsic::strip_invariant_group:
-  case Intrinsic::expect: {
+  case Intrinsic::expect:
+  case Intrinsic::expect_with_probability: {
     Register ResultReg = getRegForValue(II->getArgOperand(0));
     if (!ResultReg)
       return false;

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -7532,7 +7532,9 @@ void SelectionDAGBuilder::visitIntrinsicCall(const CallInst &I,
     return;
 
   case Intrinsic::expect:
-    // Just replace __builtin_expect(exp, c) with EXP.
+  case Intrinsic::expect_with_probability:
+    // Just replace __builtin_expect(exp, c) and
+    // __builtin_expect_with_probability(exp, c, p) with EXP.
     setValue(&I, getValue(I.getArgOperand(0)));
     return;
 

llvm/test/CodeGen/Generic/builtin-expect-with-probability.ll

@@ -0,0 +1,8 @@
+; RUN: llc < %s
+
+declare i32 @llvm.expect.with.probability(i32, i32, double)
+
+define i32 @test1(i32 %val) nounwind {
+    %expected = call i32 @llvm.expect.with.probability(i32 %val, i32 1, double 0.5)
+    ret i32 %expected
+}